Since you're interested, don't you think you need to do transient simulation? You can activate unsteady option in the "Define/Models/Solver" panel. Choose "Unsteady in the "Time" box, and "2nd-order implicit" in the "Unstesdy Formulation" box. Determine the time-step size so that you have a sufficient number of time steps (>50 e.g.,) per the expected period of the vortex shedding. Use the steady solution as an initial guess for your transient computation. See if there's any tutorial on unsteady flow simulation.